Description

An 88-year-old man was admitted to the emergency department with a head injury because of a fall. He had a loss of consciousness.
Bilateral subdural haematoma and fracture of the left parietal bone were shown on the CT imaging. The left subdural haematoma
was evacuated in operation and a drainage catheter was placed in the subdural space. His vital findings were normal in the
postoperative period. However, the patient's general condition broke down in the postoperative sixth hour. After that, cranial
CT examination was performed again. Upon CT imaging evident-increased air densities were observed in the subdural space. These
findings were consistent with the Mount Fuji sign in tension pneumocephalus (figure 1). The left drainage catheter that did not work was changed in reoperation and a new drainage catheter was placed in the right
subdural space. In the control CT examination, a significant decrease in the amount of air densities was observed (figure 2).

Axial non-enhanced CT image of brain demonstrates bilateral frontal subdural hypoattenuation with compressed and widely separated
frontal lobar tips (curved arrow). Widening of the interhemispheric space between the tips of the frontal lobes is noted.
Drainage catheter within the subdural space does not work (arrow).

Axial non-enhanced CT image of brain demonstrates resolution of the air within the subdural space after inserting a second
drainage catheter on the right side (arrow). Contusion in the deep white matter of the right frontal lobe considered as a
new sign.

The Mount Fuji sign in tension pneumocephalus is described as bilateral subdural hypoattenuating air collections which cause
compression and separation of the frontal lobes.1 The compressed frontal lobes and the widening of the interhemispheric space between the tips of the frontal lobes have the
appearance of the silhouette of Mount Fuji. The most common causes of a tension pneumocephalus are evacuation of subdural
haematoma, skull base surgery, paranasal sinus surgery, posterior fossa surgery in the sitting position and head trauma.2 It was believed that nitrous oxide, which was used as an anaesthetic, diffused into air-filled spaces and expanded the gaseous
volume.3

Learning points

The Mount Fuji sign on CT imaging of the brain is useful for differentiating tension pneumocephalus from non-tension pneumocephalus.

The most common causes of a tension pneumocephalus are evacuation of subdural haematoma, skull-base surgery, paranasal sinus
surgery, posterior fossa surgery in the sitting position and head trauma.